Just the two at Hershey for me - Wildcat and Lightning Racer.
You could see in Wildcat the direction they were going in. Trying to recreate the fantastic curves of the "lost classics" such as the Crystal Beech Cyclone, and the Fred Church Bobs coasters. Sadly, it evaded them in the case of Wildcat. I didn't think it was dreadful but was just a bit too rough and didn't quite make it on the airtime front. It was close to being good, just flawed.
Lightning Racer was brilliant though. I think they either had the right team and techniques, or with it being a racer, they concentrated on things differently.
As Marc says, it's a family thrill coaster. However, I think that's more derisive a title than it deserves. Lightning Racer was possibly the most ultimately re-ridable coaster I have ever been on - EVER. Every run was just solid fun. The airtime was small, but the pacing was just spot on. It was just a brilliant coaster to ride. No single part of it was brilliant in itself, but the overall effect was.
Sometimes things can just be great without actually ticking any of the "right boxes". The later GCI coasters seem to have got it right, with the twists, speed and airtime. Troy is an almost exact copy of a Fred Church Bobs ride - generally renowned as some of the best coasters ever made. With the modern technology and experience these guys have, it's no wonder it scores highly for most people.
So with my limited GCI experience, I say they are indeed good, particularly their latter work.